The role of adjuvant radiotherapy in stage I endometrial cancer following surgery remains unclear. The management for these patients varies widely, particularly in stage I patients with different risk factors. Using the methodology of Cochrane Collaboration, we did a systematic and meta-analysis of all know randomised controlled trials which compared adjuvant radiotherapy versus no radiotherapy following surgery for patients with stage I endometrial cancer. The meta-analysis was carried out on four trials (three published and one unpublished) and a total of 1770 patients. The addition of pelvic external beam radiotherapy to surgery reduced locoregional recurrence, a relative risk (RR) of 0.28 [95% confidence interval (CI) 0.17-0.44, P < 0.00001], which is a 72% reduction in the risk of pelvic relapse (95% CI 56% to 83%) and an absolute risk reduction of 6% (95% CI of 4% to 8%). The reduction in the risk of locoregional recurrence did not translate into a reduction in the risks of death from all causes, endometrial cancer death or distant recurrence. A subgroup analysis showed a trend towards the reduction in the risks of death from all causes and endometrial cancer in patients with multiple high risk factors (including stage 1c and grade 3). External beam pelvic radiotherapy should be considered in patients with multiple high-risk features including stage 1c and grade 3. However, it carries an inherent risk of damage and toxicity and should be avoided in stage 1 endometrial cancer patients with no high risk factors.